https://www.bloomberg.com/opinion/articles/2020-04-24/corona... "in the most severely affected regions only about 10% to 15% of the population had been infected"
So, um, no, we are nowhere near the 50 percent, at least according to any data we might have. And, depending which expert do you heed and what is the definition of "herd immunity" they're after, we need 70%, 90% or 95% before this is over.
50% would lower a 2.0 R0 to 1.0. 66% would lower a 2.5 R0 to 1.0. And this ignores that we may have permanently changed behaviors (e.g. handshakes) that facilitate spread, so we may not even need this fraction to curb tramission.
New York City is presently somewhere past 23%, so that's a big chunk of the way to a 1.0 Rt without controls.
- There is a deadly virus out there that is spreading very quickly.
- People who are not showing symptoms are spreading it.
- Community transmission has started
Given these data points, if one leader decided to lockdown sooner and another decided to wait it out, I think it is fair to say that the leader who picked lockdown made the right decision. Yes, if you add an additional data point that 50% of population is already infected, sure, you could argue that maybe it is doing more harm than good. But there is no evidence for this, and this almost certainly was not true when the lockdown decision was made in Washington and California.
The why, as Washington State Governor Jay Inslee said, "The penalties are you might be killing your grandfather if you don't do it."
It's innocent others; our grandparents, those with known compromised health conditions, and those, even young and likely uninsured, with unknown health conditions, that are being saved.
Putting this another way, I don't care if someone is a smoker in isolation. That's their choice. I care when it spreads and affects others, including myself. The balance of freedom must be considered when conflicts exist, with a bias towards preventing tragedy of the commons.
Not overwhelming hospitals.
_If_ is the key part of this sentence. We simply do not know, which is why - as you point out - testing is key!
If we were strict on lock-down and on testing, we can be very effective with this:
After a few (say 6 or 8) weeks if lock-down we can know with high likelihood who is and who is not sick. Now test all the sick people (and their friends), and start testing the general public for anti-bodies. Then start tracing any new infections.
That requires folks following the lock-down and health measures and the mass availability of virus and anti-body tests.
Real number is less than that and could be way less than that.
Lockdowns create their own form of havoc, but I think they were the right decision at the time until we had more information.
Now we need to figure a low risk way forward